The treatment of water is an issue whose impact is difficult to overstate. It impacts society as a whole through our collective need to counteract the pollution contained in wastewater and through the growing need for potable water in both industrialized and rapidly industrializing societies. Moreover, water treatment is a crucial consideration for such diverse arms of the government as NASA, which relies on the ability to recycle water in a closed loop in order to engage in even minimal space exploration, and the military, which requires simple and robust methods for providing clean water to service members deployed in regions which have underdeveloped or vulnerable water infrastructure.
A second critical, and related issue is the generation of energy. Wastewater treatment infrastructure has historically consumed approximately three percent (3%) of all electricity produced in the United States. Of the electricity produced, approximately one and one-half percent (1.5%) is used in the actual treatment of wastewater. This weakness in current wastewater treatment infrastructure is compounded in contexts where energy from outside of the water treatment facilities is hard to come by or is unreliable—such as undeveloped or underdeveloped regions of the world, in remote terrestrial environments, or in space. In such contexts, water treatment diverts energy needed elsewhere, while failures in energy provision can sabotage water treatment.
The three different commercial methods by which electricity and selective membranes are combined to remove impurities from water include; Electrodialysis (ED), Electrodialysis Reversal (EDR) and Electrodeionization (EDI). For the removal of nitrates from waste streams the process of EDR is typically used. These systems have been shown to remove nitrate from drinking water and brewery waste water. This process has the advantages of removing a range of ionic substances from water including; radium, arsenic, perchlorate, fluoride, nitrate, uranium and selenium. GE systems currently on the market have the ability to remove 40-90% of total dissolved solids and achieve up to 94% water recovery. Although EDR technology has distinct advantages over alternate technologies for the removal of ions and charged species from water sources, certain inescapable disadvantages also exist. The primary disadvantages with this technology is that it is relatively energy intensive and contaminants are not actually treated in the process but are instead concentrated into a brine stream. This brine can contain nitrate concentrations ranging from 250-2491 mg/l which invariably require down-stream treatment. This brine taken from the system is either pumped back into municipal water courses or is biologically treated on site.
Bio-electrochemical systems (BESs) are a class of technologies capable of treating water while generating electricity or other value-added products such as methane and hydrogen. Based on the ability of newly discovered microbes (termed “electricigens”) to interact electrically through direct contact with electrodes, BESs can be configured into fuel cells with living, regenerative catalysts. Fuel can include a wide range of organic substrates found in wastewater including sugars and low weight organic molecules such as ethanol and acetic acid. Because they can remove biological oxygen demand (BOD) in wastewater while generating modest amounts of electricity BESs have the potential to greatly enhance the closure and energetics of water treatment systems. BESs have the potential to function in a wide variety of capacities, such as by dynamically generating multiple useful products and by improving the efficiency of electrodialysis removal systems.